Solution Summary: Walk-Behind Masonry Saw with Vacuum Dust Control

A walk-behind masonry saw with a vacuum dust control is a mobile tool used cut concrete and other masonry materials while capturing dust.

Description:

Cutting concrete and other masonry materials generates a large amount of dust which may contain high levels of crystalline silica and creates a hazard for everyone in the vicinity. Vacuum dust controls exist for gas and electric walk-behind masonry saws. These controls consist of a vacuum, with a disposable filter (a high efficiency particulate air, HEPA, filter is often an option and recommended where practical), attached to a shroud that is compatible with the saw and partially encloses the blade. The vacuum draws air and dust from the blade, the point of dust generation, into the shroud where it is transported through tubing and into the vacuum's bag or reservoir.

Risks Addressed:

Silica dust exposure may cause silicosis or lung scarring with prolonged exposure. Silicosis is an incurable, sometimes fatal, disease. Silica has also causes lung cancer. OSHA has a new permissible exposure limit (PEL) for respirable crystalline silica in the construction industry of 0.05 mg/m3 as an 8-hour time weighted average (TWA). The NIOSH recommended exposure limit is 0.05 mg/m3 as a time-weighted average concentration for up to a 10-hour workday during a 40-hour workweek.

Another less understood, but emerging hazard is engineered nanomaterials. Incredibly small particles are being added to a broad range of construction products to improve performance, but animal toxicity tests indicate a need for closer scrutiny. There is no evidence yet that engineered nanomaterials have caused harm in exposed workers. However, it is most important that exposures be limited and that precautionary approaches be used to reduce exposure and protect construction workers from the potential hazards of engineered nanomaterials. Nano-size ultrafine titanium dioxide, which can be present in nano-enabled masonry products, has been found to cause inflammation of the lungs and lung cancer in lab animals. The National Institute for Occupational Safety and Health (NIOSH) has determined that ultrafine titanium dioxide should be considered a potential occupational carcinogen. Other engineered nanomaterials that may be present in nano-enabled construction materials used in masonry work could also have the potential to cause harm when inhaled by construction workers. It has been demonstrated that cutting nano-enabled concrete roofing tiles without vacuum dust controls using hand-held masonry saws can generate excessive amounts of airborne dust that if inhaled by workers could increase the risk of developing respiratory disease (West GH, et al 2016). Excessive amounts of airborne dust would also be expected when a walk-behind masonry saw is used without vacuum dust collection.

OSHA has no specific regulation or Permissible Exposure Limit (PEL) for any engineered nanomaterial. However, NIOSH has a recommended exposure limit (REL) for ultrafine titanium dioxide of 0.3 mg/m3 as a time-weighted average (TWA) concentration for up to 10 hours/day during a 40-hour week. The intent of the REL is to lower the risk to workers of the potential for developing lung cancer.

How Risks are Reduced:

The shrouds partially enclose the blades of the saws and have a connection for a vacuum system. When a vacuum system is connected to the shroud, air is drawn into the shroud and past the blade, capturing dust and silica at the point of dust generation. The system captures dust and silica near the source, reducing concentrations in the worker's breathing zone and his or her exposure.

The Blastrac website (www.blastrac.com/en-us/c-20-masonry-tile-concrete-saws.aspx) states that its walk-behind masonry saws use "dry diamond blades to save time on cleanup" and feature "a blade guard designed with upcut rotation to allow for easy dust extraction and quick connection to a dust collection system."

No specific reports have evaluated the effectiveness in reducing exposures to engineered nanomaterials of walk-behind masonry saws equipped with vacuum dust collection (VDC). However, vacuum dust collection would also presumably be very effective in reducing exposures to engineered nanomaterials because it has been demonstrated that VDC is capable of substantially reducing exposures to silica and respirable dust.

A study conducted by CPWR – The Center for Construction Research and Training demonstrated that local exhaust ventilation (LEV) attached to a hand-held masonry saw was effective in substantially reducing exposures to both respirable dust and titanium dioxide while cutting nano-enabled concrete roofing tiles that contained titanium dioxide. Tiles were cut completely through in a controlled chamber setting and in the absence of vacuum dust controls, excessive amounts of visible dust was generated. When LEV was used, statistically significant reductions in mean concentrations of respirable dust and airborne titanium dioxide were obtained. Reductions in mean exposure concentrations were 95% or greater when LEV was used and the concentrations of airborne titanium dioxide were below the NIOSH REL for both fine (2.4 mg/m3) and ultrafine (0.3 mg/m3) titanium dioxide. (West GH, et al 2016). While this study evaluated the impact of a dust collection system on a handheld masonry saw instead of a walk-behind masonry saw, it does provide evidence that local exhaust ventilation techniques are likely to be quite useful in reducing engineered nanomaterials exposure when used with walk-behind masonry saws.

Effects on Productivity:

Vacuum dust control systems can have either positive or negative effects on productivity. However since use of vacuums eliminates large amounts of both airborne and settled dust, they provide a cleaner, more efficient means of masonry cutting.

Improved visibility can improve quality and productivity. Dust capture greatly reduces site cleanup times. Dust capture avoids exposing other workers, members of the public, adjacent property, cars and building occupants, which can be associated with increased liability and time consuming disputes. Improved worker comfort is a result of reduced dust which may in turn result in less fatigue for the worker and greater productivity. In some cases, particularly where saw use is intermittent, vacuum dust control may be adequate to reduce the need to wear a respirator, and the need for an employer respiratory protection program.

Some additional issues should be considered. Changing vacuum bags takes time, which will depend on the amount of cutting being done and the size of the vacuum bag or hopper. Workers will need to adapt to working with a vacuum hose attached to the tool. Saw and vacuum energy requirements may exceed the capacity of a single standard 20 Amp circuit when combined requiring access to two circuits or special wiring.

Additional Considerations:

Ventilation for construction tools is often misunderstood. There are some key concepts that can help:

The vacuum must be located as close to the dust generation as possible to be effective. A shroud may be needed to contain the dust so the vacuum can capture it. The shroud must be kept as close to the work surface as is practical to provide adequate dust capture.

The particles that can do the most damage in the lungs are small enough to penetrate the filters found on many shop vacuums. Additionally, some inexpensive shop vacuums pull the dust through the motors, which can destroy the vacuum on really dusty jobs, eliminating any initial cost savings.

For dust containing harmful particles like silica, it is important to use as high efficiency filters as practical. The best available are called HEPA (High Efficiency Particle Air) filters because they capture 99.97% of the most penetrating particles. But HEPA filters also create a greater pressure drop and decrease in air flow rate because it is more difficult to pull air through these denser filters so capture velocity may be reduced. They also require pre-filters to extend the life of the HEPA filters, which are more expensive than other filters. Studies have shown that it may be more effective to direct the exhaust air out of the work area than to attempt to add HEPA filtration for a tool where it isn't an integral part already. HEPAs require routine disposal of prefilters, which can cause exposures to those doing the filter change out.

For operations that generate large amounts of dust, cyclonic collection units, if available, may be the best solution. Rather than require more expensive filters and bags that must be frequently changed, cyclonic units spin the particles and drop them into cheap bags that need to be replaced far less frequently because loading of the bags does not cause a pressure drop.

Vacuum performance must be monitored on a regular basis. For high dust generating tasks, dust caked on the filter may reduce flow to a level where it no longer provides adequate dust capture. Automatic and manual filter shakers, coarse pre-filters and cyclonic collections units are available with some vacuums and may help maintain the air flow rate.

Large electric vacuums commonly require 20 amp electrical circuits in addition to the 20 amp circuit used for the electric masonry saw. Cords and extensions must be rated for the tool's power requirements, be inspected regularly, and used in combination with ground fault interrupt circuits.

The use of gasoline-powered equipment poses the risk of carbon monoxide exposure, particularly in areas where airflow is reduced. Steps to control exposure are important because the gas is invisible, odorless and tasteless. Small, inexpensive personal monitors can be worn by the operator to warn of unacceptable exposures.

Walk-behind masonry saws frequently generate sound levels that are greater than 90 decibels, the OSHA Permissible Exposure Limit (PEL), and hazardous. Hearing protection should be worn when using masonry saws unless an industrial hygienist has conducted noise monitoring and indicated that hearing protection is not required.

As is the case with any construction equipment, users should follow manufacturer safety recommendations and comply with any applicable local, state or federal regulations. Many cities have ordinances that prohibit release of visible dust as a public nuisance. Vacuum dust collection systems may provide a mechanism for compliance.

Personal Protective Equipment

Work practice

Return on Investment

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